In Traditional Chinese Medicine (TCM), Mei Gui Hua belongs to the 'Herbs that regulate Qi' category. Herbs in this category typically treat a TCM condition called 'Qi Stagnation'. Concretely it means that Qi is blocked in the body's Organs and Meridians, most typically the Stomach, Liver, and to a lesser extent, the Lungs. In modern medicine terms, Qi Stagnation often translates into psychological consequences such as depression, irritability or mood swings. It's also frequently associated with conditions such as premenstrual syndrome (PMS), menopausal symptoms, the development of breast swellings as well as various digestive disorders.
Furthermore Mei Gui Hua is Warm in nature. This means that Mei Gui Hua tends to help people who have too much 'Cold' in their body, although with less effect than a plant that would be Hot in nature. Balance between Yin and Yang is a key health concept in TCM. Those who have too much Cold in their body are said to either have a Yin Excess (because Yin is Cold in nature) or a Yang Deficiency (Yang is Hot in Nature). Depending on your condition Mei Gui Hua can help restore a harmonious balance between Yin and Yang.
Mei Gui Hua also tastes Bitter and Sweet. The so-called 'Five Phases' theory in Chinese Medicine states that the taste of TCM ingredients is a key determinant of their action in the body. Bitter ingredients like Mei Gui Hua tends to have a cleansing action on the body by clearing Heat, drying Dampness and promoting elimination via urination or bowel movements. On the other hand Sweet ingredients tend to slow down acute reactions and detoxify the body. They also have a tonic effect because they replenish Qi and Blood.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Mei Gui Hua is thought to target the Liver and the Spleen. In TCM the Liver is often referred as the body's "general" because it is in charge of regulating the movements of Qi and the Body Fluids. It also takes a leading role in balancing our emotions. The Spleen on the other hand assists with digestion, Blood coagulation and Fluids metabolism in the body.